News this week of the discovery of a "superbug" was startling because such a bacterium, resistant to all forms of antibiotic medicine, had not previously been encountered in the United States.

The head of the U.S. Centers for Disease Control and Prevention, Dr. Tom Frieden, says this new bug is resistant to every antibiotic in a physician's arsenal of drugs, including Colistin.

Colistin has become the antibiotic of last resort for American physicians fighting what Frieden calls "nightmare bacteria," even though its toxic side-effects potentially include liver damage. The drug, known since the 1950s, has come into increasing use because it usually is effective against antibiotic-resistant bacteria.

That changed last month, however, when doctors in the state of Pennsylvania found that a woman they were treating was infected by a form of E. coli bacteria, known as CRE, that contain a gene resistant to colistin. This phenomenon has occurred in other parts of the world previously, but never before in the United States.

In the worst case, the CDC says, this could lead to the "emergence of truly pan-drug resistant bacteria" - microbes that would be impervious to any drug physicians can deploy against them.

Role in bacteria

Antibiotic drugs are prescribed to fight and kill invading bacteria in several different ways: they can destroy a bacterium's cell wall, or prevent bacteria from repairing damage to their cells, or they can disrupt bacterial reproduction, which in turn would stop an infection from spreading.

Even after a patient with an infection receives a course of antibiotics, in most cases some small number of bacteria remain. These could be organisms that have mutated, or evolved, to a form that allows them to survive antibiotic treatment.

U.S. health authorities estimate antibiotic-resistant bacteria sicken 2 million Americans a year, and 23,000 of them die.

Herman Goossens, a professor of medical microbiology at Belgium's University of Antwerp, told VOA the likelihood of bacterial mutations increases when doctors prescribe "a cocktail" of several antibiotic drugs to fight an unidentified infection.

Life finds a way

This practice, also known as "overprescribing," increases the possibility that the bacterial infection will mutate or evolve - changing its cellular and genetic structure to make the bacteria resistant to the antibiotic being used. As resistant bacteria multiply and spread to other patients, eventually that antibiotic becomes useless.

"That's all wrong," Goossenns says, "...This practice has to change.”

Drug manufacturers spend large sums of money on research aimed at finding new and more effective antibiotics, and new infection-fighting also are being studied.

The journal Nature reported this week that researchers at several U.S. universities suggest that viruses can be used to attack invading bacteria.

Anti-bacterial viruses, also jknown as "bacteriophages," can specifically target and kill bacteria, Nature reported. And when the viruses bind to the surface of individual bacteria, the researchers say they also negate the bacteria's drug resistance - in effect, making old drugs new and effective again.